Use Knob disabled in Vector Configuration

Having switched to a Spektrum DX9 transmitter (specifically to use the knob for gain control) I am unable to select any of the "Use Knob" selections for any of the gain settings in the Vector Configuration tool. The knob is configured and operational in the RC Configuration page and I am able to rotate it on the transmitter and see the change on the Gain Knob graphic display. I am also able to see the Gain Knob values change in the OSD. But for some reason I am unable to select any of the "Use Knob?" selections to actually use it.

I am using a Micro Vector v12.60 with firmware v2.65 connected to a Spektrum SPM4648 Serial Receiver. The Micro Vector is configured for Elevon Fixed Wing and I have run the Rx Analysis Wizard several times trying different changes of the knob during the analysis with no changes in the selections for the "Use Knob?". They are all simply disabled and greyed out at all times.

So, what am I doing wrong and what did I miss in the documentation that is causing this condition?

Hi John, thank you for your reply. Upon further reading I started to get that idea but was thrown off by the fact that the settings all said 'No' for "Use Knob?" selections even though they were disabled from being selected.